The letter says: 'If the police are serious about ensuring that Muslim officers are able to rise through the ranks at the same speed as their fellow white officers, and ensuring that Muslims are deployed to counter-terrorism duties at a time of heightened national security, we must have reliable data to track progress and measure success.' It adds that the 'paucity' of information 'means that each individual case of discrimination, or alleged discrimination, can only be assumed to be symptomatic of the conditions facing Muslim officers across the UK'.